In early 1920's, a German engineer, Anton Flettner, invented Magnus rotors that used a Magnus effect to propel an aquatic vessel. The Magnus effect may be defined as a thrust acting on a rotating body in a moving airstream, such as wind, wherein the thrust acts perpendicularly to a direction of the moving airstream.
The Magnus rotors were not received well by mariners of that era, as fuel was inexpensive and the mariners preferred to use standard marine propellers in preference to the Magnus rotors.
However, with passing time, fuel prices have increased rapidly and considerably, for reasons of “peak oil” (ref. Hubbert peak theory by Marion King Hubbert) and increasing demand as the World's population presently increases in a substantially exponential and uncontrollable manner. Today, the marine industry is making new attempts to harvest wind power to supplement standard marine propellers to propel aquatic vessels.
Typically, a thrust generated by a Magnus rotor depends on a rate and a direction of rotations of the Magnus rotor relative to an apparent speed and an apparent direction of wind. As wind conditions change regularly during a course of a journey of an aquatic vessel, the rate of rotations of the Magnus rotor needs to be adjusted repeatedly with changing wind conditions in order to maximise propulsion from the Magnus rotor.
The terms “apparent wind speed” and “apparent wind direction” refer to wind speed and direction as observed from an aquatic vessel in motion. In case when the aquatic vessel is stationary, the apparent wind speed and the apparent wind direction are the same as the wind speed and the wind direction in relation to Earth or a fixed object. Measurement of the apparent wind speed can be done technically by employing an anemometer and/or other wind sensors. The wind speed and direction in respect to the fixed object or Earth can be calculated from the measured apparent wind by taking in account speed and direction of the aquatic vessel.
A conventional propulsion system for adjusting a rate of rotations of a Magnus rotor has been provided in U.S. Pat. No. 8,230,798. The rate of rotations of the Magnus rotor is adjusted, based on an apparent wind speed measured with an anemometer. The apparent wind speed is taken as a mean apparent wind speed for a specified period of time.
Another conventional propulsion system for adjusting the rate of rotations has been provided in Canadian patent application no. CA2811249. The patent application discloses a ship with multiple Magnus rotors. The rate of rotations of the Magnus rotors is adjusted, based on the measured apparent wind speed and the measured apparent wind direction, a predetermined destination of the ship and/or navigation information.
However, these conventional propulsion systems suffer from a number of disadvantages. Firstly, rotating parts of the Magnus rotors may be large in size and may weigh from a few tonnes to several tonnes. Therefore, adjusting the rate of rotations of the Magnus-type rotors, namely a rotational energy of the rotating parts, may require a large amount of energy. Secondly, the rate of rotations is adjusted based on the apparent wind speed and the apparent wind direction measured at a current time. Therefore, a lesser amount of time is available to the conventional propulsion systems for adjusting the rate of rotations. This, in turn, increases power consumption of the conventional propulsion systems considerably. Moreover, this may pose additional problems in cases where wind conditions change rapidly.
In light of the foregoing discussion, there exists a need for a propulsion system for an aquatic vessel that is capable of facilitating an improvement in propulsion, while reducing associated power consumption, as compared to known conventional propulsion systems.